The phenomenon of electrical induction, i.e., the interaction between electrical and magnetic fields to generate a force or create current flow, is exploited in a wide number of applications across a substantial range of industries. Indeed, in almost all cases where electrical energy is generated or is converted to physical motion, the power of electrical inductance is employed.
For example, the spinning of a magnetic array within a network of conductors (or the spinning of conductive coils within an array of magnets) generates a current flow that can be harnessed as usable electric power. This principle is at work in generators in industrial applications, automotive applications, municipal power applications, and so on. Conversely, in motor applications, when an electric current is forced through a conductive coil, the magnetic field thus induced interacts with a permanent magnetic field to cause movement of the coils (or the permanent magnets).
While the desired effects of the inductance phenomenon, i.e., the generation of power or the inducement of physical motion, are generally beneficial, there are sometimes also unintended consequences due to parasitic induction. A pertinent example of this is what is sometimes known as shaft charge or shaft discharge. In this situation, a spinning shaft used in a power generation or motor application becomes inductively charged relative to a nearby grounded body, i.e., the motor housing or generator housing. While the static charge thus created is not in itself detrimental, the charge may suddenly dissipate, or arc, through an intermittent path to ground at a certain voltage level. The voltage level at which this occurs is dependent upon many factors, ranging from the humidity of the air to the conductivity of the various components of the machine. However, in most cases, this discharge can be harmful and is generally undesirable.
In particular, the sudden discharge is often at a significant voltage amplitude, albeit of a very brief duration. During this brief high-voltage discharge, the components through which the charge travels may be etched, pitted and even burned. This is because electrical discharge is a nonlinear threshold phenomenon. In other words, the first available conductive path will allow the immediate onset of discharge, which will further diminish the likelihood of the discharge taking any other path, even when those other paths are almost identical. Thus, in analogy to spot welding, the first even marginally suitable discharge path is forced to accommodate the entire discharge, resulting in rapid heating and melting of even the strongest conductive materials. Indeed, even the hardest metallic bearings can be rapidly etched and pitted by this phenomenon.
The possibility of destructive shaft discharge has long been known, and many attempts have been made over the years to eliminate this problem. Although some solutions have been somewhat effective, there has yet to be a solution that is fully effective, economical, and relatively maintenance free.